Algebraic entropy is as a test of integrability for discrete systems. Given a bi-rational map, which can be an ordinary difference equation, a differential difference equation or even a partial difference equation, the basic idea is to examine the growth of the degree of its iterates, and extract a canonical quantity, which is an index of complexity of the map. This canonical quantity will be the algebraic entropy (or its avatar the dynamical degree) [1]}, [2]}, [3]}, [4]}, [5]}. In [6]}, [7]} the method was developed in the case of quad-equations and then used as a classifying tool [8]}. A slight generalization of the method was given in [9]} where it was showed that non-autonomous equations can have more that a single sequence of degrees.
